Over the past several decades, there has been an increasing demand among dentists and dental patients for more aesthetic dental restorations. The dental industry's growing focus on aesthetic dentistry has led to the development of dental restorative compositions that more closely mimic the appearance of natural teeth. For example, tooth-colored, composite resin materials have been developed that can be used in place of, for example, metal amalgam fillings, to provide more natural looking dental restorations. In recent years, highly aesthetic composite materials containing silica and/or zirconia nanofillers have become available with shading systems and opacity options that make it possible for a dentist to create dental restorations so natural looking they are virtually undetectable to the casual observer.
Natural tooth enamel has an opalescent quality to it in that it preferentially bends the shorter (blue) wavelengths of light, appearing bluish against a dark background, and more orange/yellow against a white background. Although opalescent dental composites have been developed, this property is often lacking from dental composites that use a silica-zirconia nanofiller system. Despite the many beneficial properties offered by silica-zirconia nanofillers, lack of opalescence may be seen as a drawback. Thus, there remains a need for filler systems, especially silica-zirconia nanofiller systems, that provide dental composites having opalescent properties to better mimic the appearance of natural teeth, while still maintaining suitable handling, radiopacity, clarity, translucence, and other desirable properties of dental composites.